This all started last year with the Motorola-made Nexus 6, which featured bands that work with all four of the US carriers. That included the CDMA carriers Sprint and Verizon. The Moto X Pure Edition was the same way earlier this year, and during our review we used it on both Verizon and T-Mobile. Now when the Nexus 5X and Nexus 6P were announced last month in San Francisco, Google did state that they both worked with all four US carriers (also that none of the carriers would be selling them this time). However, when it comes to these things - similar to the cameras, in which manufacturers always tout how awesome their cameras are, which aren't always the truth - we had to test it out to be sure.
It appears that the Nexus 5x and Nexus 6P both work flawlessly on Verizon. However, there is a caveat, and one that you probably saw coming. It only works with activated Verizon SIM cards. And not new ones. Simply because these devices aren't in Verizon's system, so they aren't whitelisted. Verizon also still doesn't sell just SIM cards, like GSM carriers - T-Mobile and AT&T - have done for years and years. So if you were looking to jump ship over to Verizon and use one of the new Nexus' as your new device, well that's not going to work. At least not yet, that could change in the future. However, if you already have a line on Verizon and want to "upgrade" to a Nexus 5X or Nexus 6P, just pop in your SIM from your current device, and you'll be all set to go in a few moments.
Once you pop in the Verizon SIM into your new Nexus device, it'll use the appropriate APN, and you'll be all set and ready to go. You don't even need to reboot the device, which is pretty convenient. Sprint should work exactly the same, however we don't have a Sprint SIM on hand to test out. And of course, AT&T and T-Mobile SIMs can be popped in like normal. That isn't really news there, as we've been able to do that with GSM carriers for a long time.